The second method I like more. If at the end of the RAW development one could export a 16 bit Tiff in pRGB to Qimage Ultimate, little would be lost and the file can be kept there for different jobs. But I wonder whether that still is a good idea if one imports it in Photoshop for more image editing on the 16 bit Tiff. Is that gamut not just covering the best printers' gamuts?
Hoi Ernst,
Yes, it's supposed to cover all printer media gamuts, but it's not nearly as small as an Adobe RGB gamut, it is instead still reasonably big. When I plot Adobe RGB, pRGB, and ProPhotoRGB colorspaces, the Argyll CMS 'Viewgam.exe' reports a gamut of:
1209647.5 cubic units for AdobeRGB 1998 (100% inside the pRGB colorspace),
1779999.8 cubic units for pRGB (68% intersected by AdobeRGB, so 32% larger, and 100% inside the ProphotoRGB colorspace),
2893604.8 cubic units for ProPhotoRGB (61.6% intersected by pRGB, so another 38.4% larger but partly imaginary 'colors').
The PS edits may have an influence on the boundaries of that gamut which might not cover the best output gamuts as nice anymore?
Yes, in theory one could push colors outside the pRGB gamut by editing, but it would not make sense to do so, because the colors cannot be printed. With a bit of luck, a perceptual rendering intent will pull them back into gamut, but also alter many other colors.
Luckily, it is rarely an issue because actual image colors in a file usually only occupy a small percentage of the full gamut of pRGB. Only those colors exactly on the axes of the primaries of the colorspace run a risk of being edited into an OOG color, others will just map to previously unused coordinates with lots of room to spare. It is really an eye-opener to see how little colorspace an image occupies.
To view it from another angle, Luc's 'torture_test.tiff' image, in ProPhotoRGB and with pushed saturation, intersects for 92.19% with the pRGB colorspace. Only a few very dark blue colors risk being clipped to marginally brighter very dark blue colors. In comparison, that image intersects for 92.22% with the ProPhotoRGB colorspace, only 0.03% additional colors are encoded, the rest of the coordinate space is unused and reserved for imaginary 'colors' we can't even see, and certainly not print/display, and with much coarser quantization steps to cover the (98.3% for nonexisting image colors) distance. The image only occupies 2.76% of the pRGB gamut, and 1.7% of the ProPhoto RGB colorspace.
pRGB is plenty large enough, but not insanely so.
With extended RAW developers like RawTherapee the route to a Tiff image editor is less needed, a RawTherapee pRGB conversion in the Tiff export can be done at best conditions if I interpret its features correctly.
Correct, but the risk of overcooking the colors remains very small, even with an additional editor step. pRGB offers hardly any downsides (why create an unprintable color anyway), but many upsides (more accurate, denser quantization, less risk of posterization in an 8-bit pipeline). The added dithering in Qimage reduces the posterization risks even further.
Cheers,
Bart